To be honest, while 8 Healers sounds like a pretty big problem, just come at them with a lot of BLMs. Sleep them all, then pick 'em off one-by-one. While it's just a theory, it sounds like a pretty hard counter to me.

Also, not to argue semantics (but I will), an "exploit" would be using something in the game that isn't meant to exist, like the height exploit in the Terrotaur fight before it was fixed. This party composition is merely an obnoxious, if incredibly effective, strategy, haha!